The present invention relates to lost wax casting of thin walled hollow objects, especially metal golf club heads, more particularly to the molding process for creating the wax pattern of the club head to be cast, and even more particularly to a core for; a wax mold that can be readily stripped from the mold without first removing the wax pattern therefrom.
Many golf clubs, in particular the metal woods, have hollow metal heads with precisely formed thin walls to provide advantages in striking a golf ball. Typically such heads are made by lost wax casting. Precision is required in the casting process in order to ensure that precise dimensions are maintained so that the final product incorporates the advantages which may be achieved from the thin walled head. Such thin walls have created difficulties in the casting process due, at least in part, to the need to provide a core to create the hollow wax pattern, which core must be stripped from the wax pattern before use. The typical prior art process required a skilled operator to open the wax pattern mold and remove the core from the wax pattern by hand. Such hand stripping of the core often causes deformation or other damage to the wax pattern, which jeopardizes the precision of the casting.
A wax pattern molding process using a stripable core which attempts to address some of these difficulties with the prior art is described in U.S. Pat. Nos. 5,204,046, 5,417,559 and 5,547,630. In these patents, a molding process is described in which a core made of multiple pieces, held together by T-shaped sliding interconnections, is wedged within a double door mold. One door of the mold creates at least part-of the mold cavity and the second door has a wedge which forces the core in place within the cavity. While addressing certain difficulties with stripping of the mold, this solution is not ideal. In particular, the wedging action which holds the core in place does not necessarily guarantee the precise positioning of the core due to inconsistencies as a result of force application being dependent on the degree of mold closure in such a wedging arrangement. Also the double door configuration adds complication to the mold. There thus remains a need in the art for an easily stripable mold which locates the core with precision.
It is therefore an object of the invention to provide a wax pattern mold with a stripable core that permits greater control over dimensional integrity of the walls of hollow thin walled objects to be molded.
This and other objects are achieved according to the present invention by a mold which comprises a mold body and a mold core. The mold body is made up of at least two mating parts together defining a cavity configured and dimensioned to define the outside of the hollow object to be molded, preferably the wax pattern of a metal wood golf club head. The mold parts also define a channel for delivering molten wax to the cavity and an opening configured and dimensioned to receive the mold core therethrough and extending into the cavity. The mold parts are separable to remove the molded object. In a preferred embodiment, the mold body parts are two halves hinged together for opening and closing.
The mold core has an upper portion configured and dimensioned to define the inside of the hollow object to be molded and a stem portion configured and dimensioned to be received in the mold body opening and mate with the mold body parts. The core is made up of a plurality of interfitted parts configured and dimensioned to be sequentially removable through the mold body opening without opening the mold halves. Also part of the invention are means for registering the position of the mold core in the mold cavity, and means for locking the core parts together.
According to one embodiment of the invention, the registering means comprises at least one registration member extending out from the core stem and at one least recess defined in the mold body around the mold body opening to receive the registration member in close fitting, positive engagement. In various alternative embodiments the registration member is a ridge formed at least partly around the core stem, at least one pin extending out from the core stem or a key extending out from the core stem wherein the recess receiving the registration member is a keyway.
In another alternative embodiment the registering means comprises at least one registration member extending out from the mold body around the mold body opening and at least one recess defined in the core stem to once again receive the registration member in close fitting, positive engagement. The same alternatives are again possible, in opposite relationship.
According to a further aspect of the invention, locking means comprises an extendable locking finger mounted on one core part and a slot for receiving the finger defined in a mating core part. In an alternative embodiment, locking means may comprise a locking member and at least one slot for receiving the locking member, wherein the slot is formed in one of the mold parts and the locking member bears against the core to lock the core in position when received in the slot. According to this alternative, the locking member may comprise an extendable locking finger disposed on an outer surface of the core, the finger being extendable from the core to be received in the slot, or a locking gate, slidably received over the core in two opposed slots defining in the mold parts. In further alternative embodiments, the locking means may comprise dowels inserted through close-fitting holes in the core stem portion to lock the parts together, either through the mold body or outside the mold body, or a locking gate carried in grooves in the mold body that bears against the mold stem portion.
The core according to the invention also may comprise a base plate with one of the plurality of core parts fixed thereto and a plurality of upstanding pins also fixed to the base plate. In this embodiment the other core parts have holes defined in them to receive the pins such that the parts may be removably assembled over the pins.
A further aspect of the invention is a method for forming a wax pattern of a hollow, thin walled object, such a golf club head, including the following steps: providing a wax pattern mold made up of at least two parts together defining a cavity configured and dimensioned to form the outside of the wax pattern, placing in the mold cavity a core configured and dimensioned form the hollow inside of the wax pattern wherein said core is comprised of multiple core parts, said placing including registering the core with the mold cavity to ensure dimensional integrity of the thin walls of the object, closing the mold parts together, locking the multiple core parts together in a step separate from said placing step, flowing molten wax into the mold cavity, permitting the wax to harden to form the thin walled wax pattern, removing the core while maintaining mold parts closed, opening the mold parts, and removing the wax pattern.